Pulse-dividing method and apparatus for a pulsed carbon monoxide laser

Abstract

Laser-drilling apparatus includes a gas-discharge for laser emitting laser-radiation pulses, and two acousto-optic modulators (AOMs). The laser radiation pulses are characterized as having two temporal central portions between temporal leading and trailing edge portions. The AOMs are arranged to spatially separate the central temporal portions of the pulses from each other and from the leading and trailing edge portions of the pulses.

The invention claimed is: 
     
       1. Apparatus for laser-drilling a work-piece, comprising:
 first and second acousto-optic modulators (AOMs); 
 a carbon monoxide (CO) laser emitting laser-radiation pulses with radiation in the pulses having a plurality of wavelengths in a wavelength range between about 4.5 micrometers and about 6.0 micrometers, the laser-radiation pulses having a temporal rising-edge portion, a temporal falling-edge portion, and first and second temporal central portions therebetween, and the laser radiation pulses being incident on the first AOM in a first incidence direction; 
 the first AOM being arranged and operated to receive the laser-radiation pulses and to diffract the temporal rising- and falling-edge portions and one of the first and second temporal central portions of the pulses along first wavelength-dependent first-diffraction-order directions at angles to the first incidence direction, said diffracted portions of the pulses being angularly dispersed as a function of wavelength, said first AOM transmitting the other of the first and second temporal central portions of the radiation pulses along a first zero-order direction parallel to the first incidence direction; and 
 the second AOM being arranged and operated to receive the diffracted pulse-portions from the first AOM, diffract the other of the first and second temporal pulse portions along second wavelength-dependent first diffraction-order directions, and transmit the temporal rising- and falling-edge portions along second zero-order directions at an angle to the second wavelength-dependent first diffraction-order directions with the first and second temporal central portions being used for drilling the work-piece and wherein the diffraction by the second AOM reduces the angular wavelength dispersion of the temporal portion of the pulse created by diffraction in the first AOM. 
 
     
     
       2. The apparatus of  claim 1 , wherein the first and second AOMs are arranged and operated such that the first zero-order direction and second wavelength-dependent first diffraction-order directions are about parallel to each other. 
     
     
       3. A method of slicing laser pulses with first and second acousto-optic modulators (AOMs), each of said laser pulses having a temporal rising-edge portion, a temporal falling-edge portion, and first and second temporal central portions therebetween, said laser pulses being generated by a carbon monoxide laser emitting laser-radiation pulses with radiation in the pulses having a plurality of wavelengths in a wavelength range between about 4.5 micrometers and about 6.0 micrometers, said method comprising the steps of:
 directing a pulse to the first AOM; 
 during a first time period, activating the first AOM so that the temporal rising-edge portion of the pulse is diffracted along a path to the second AOM, and during said first time period, deactivating the second AOM so that the temporal rising-edge portion of the pulse is not diffracted and is directed to a beam dump; 
 during a second time period, deactivating the first AOM so that the first temporal central portion of the pulse is not diffracted and is directed along a path to a work-piece; 
 during a third time period, activating both the first and second AOMs so that the second temporal central portion is diffracted by both the first and second AOMs and is directed along a path to a work-piece and wherein angular wavelength dispersion induced by diffraction in the first AOM in the second temporal central portion is compensated by diffraction in the second AOM; and 
 during a fourth time period, activating the first AOM and deactivating the second AOM so that the temporal falling-edge portion of the pulse is diffracted by the first AOM and not diffracted by the second AOM and is directed to a beam dump. 
 
     
     
       4. The method of  claim 3  wherein the first and second AOMs are positioned such that the path of the laser pulse exiting the first AOM when the first AOM is deactivated is parallel to and spaced apart from the path of the laser pulse exiting the second AOM when the second AOM is activated. 
     
     
       5. A method of slicing laser pulses with first and second acousto-optic modulators (AOMs), each of said laser pulses having a temporal rising-edge portion, a temporal falling-edge portion, and first and second temporal central portions therebetween, said laser pulses being generated by a carbon monoxide laser emitting laser-radiation pulses with radiation in the pulses having a plurality of wavelengths in a wavelength range between about 4.5 micrometers and about 6.0 micrometers, said method comprising the steps of:
 (a) directing a pulse to the first AOM; 
 (b) during a first time period, activating the first AOM so that the temporal rising-edge portion of the pulse is diffracted along a path to the second AOM, and during said first time period, deactivating the second AOM so that the temporal rising-edge portion of the pulse is not diffracted and is directed to a beam dump; 
 (c) during a second time period, performing one of steps (d) or (e) 
 (d) deactivating the first AOM so that one of the first and second temporal central portions of the pulse is not diffracted and is directed to a work-piece; or 
 (e) activating both the first and second AOMs so that the one of the first and second temporal central portions is diffracted by both the first and second AOMs and is directed to a work-piece and wherein angular wavelength dispersion induced by diffraction in the first AOM in said one temporal central portion is compensated by diffraction in the second AOM; 
 (f) during a third time period, performing the other of steps (d) or (e) on the other temporal central portion of the pulse; and 
 (g) during a fourth time period, activating the first AOM and deactivating the second AOM so that the temporal falling-edge portion of the pulse is diffracted by the first AOM and not diffracted by the second AOM and is directed to a beam dump.